This invention relates to a connector for connection of a digital signal line and, in particular, to a connector to be mounted to a board or the like.
As a digital transmission system, a TMDS (transition minimized differential signaling) is known. In the TMDS, a digital signal is transmitted by a pair of two signal lines and one ground line.
As modes of digital signal transmission, an unbalanced (single-end) type and a balanced (differential) type are known. In the unbalanced signal transmission, a high level and a low level of a digital signal are distinguished by a potential difference between a ground line and a signal line (one). In the balanced signal transmission, a high level and a low level of a digital signal are distinguished by a potential difference between two signal lines (+, −).
In the balanced signal transmission, two signals on the two signal lines are equal in voltage level to each other and different in phase by 180° from each other. Therefore, even if noise is produced in the two signal lines, the noise is cancelled at a receiver input stage. Thus, as compared with the unbalanced signal transmission, it is easily possible to improve transmission accuracy.
Japanese Patent No. 3564555 (JP-B) discloses a connector for use in the balanced signal transmission. The connector comprises a plurality of contact sets each of which includes a + signal contact and a − signal contact connected to two signal lines, respectively, and a ground contact connected to a ground line. In each contact set, the + signal contact and the − signal contact are arranged symmetrical with respect to the ground contact to form an isosceles triangle. The contact sets are arranged in a single row so that bottom sides of the isosceles triangles are alternately arranged in a staggered fashion. Namely, the isosceles triangles are alternately inverted in position.
In a fitting portion to be fitted to a mating connector, contacting portions of the contacts are arranged in two rows at equal pitches. In each row, the contacts are arranged in a manner such that one + signal contact and one − signal contact are adjacent to each other and one ground contact is arranged next.
On the other hand, at terminal portions to be connected to a board, the contacts are arranged in three rows. The + signal contacts and the − signal contacts are arranged in opposite peripheral rows at equal pitches, respectively, while the ground contacts are arranged in a middle row at equal pitches. Thus, the contacts are arranged in two rows at the contacting portions in the fitting portion and in three rows at the terminal portions. In other words, a pitch-conversion of the contacts is carried out between the contacting portions and the terminal portions.
At the terminal portions, the contacts are connected to wiring patterns formed on the board. The wiring patterns may be formed to extend through a space between adjacent ones of the contacts. For example, two wiring patterns connected to two + signal contacts may be required to pass through a space between two adjacent − signal contacts. In this case, if the space between the two adjacent − signal contacts is narrow, it is difficult to make the two wiring patterns pass therethrough.
In addition, the pitch-conversion might causes differences between the + signal contact and the − signal contact in their lengths and between the signal lines in their lengths. These differences result in occurrence of skew known in the art.